Using the compilation of thousands of DLAs from SDSS
[1]}, we have selected a subset
having high H i column density, with log \(N\)(H i)\(\rm [cm^{-2}]\) 
\(\ge 21~\rm \) , which provides the favorable environment for star
formation and thus is likely to trace regions in close proximity to
star-forming galaxies
[2]}, [3]}.
Moreover, at these high column densities, the Ly\(\alpha \)  absorption
has a dark (optically thick) core, which spreads
over at least 7 times the average full-width at half-maximum (FWHM,
\(\approx \)  160 \( \rm km~ s^{-1})\)  of the instrumental profile of the
SDSS spectrograph. This makes it possible to search for Ly\(\alpha \)   emission
lines within the spectrum.
